According to the Malbim, Esther sent Mordechai clothing because he needed to be dressed properly to enter the palace, and she wanted to hear the information directly from him. This would be especially true if, as the Vilna Gaon surmises, Esther thought the information in question was confidential.
R’ Dovid Feinstein, however, writes that Esther sent clothes to Mordechai because she felt he was over-reacting; she felt confident that she could overpower Haman within the remaining eleven months before the given date of the Jews’ destruction.
Interestingly, Tiferes Shlomo takes this incident as indicative of the classic argument on Judaism – should one fast and practice asceticism, or should one fulfill the words of Tehillim in striving to “ivdu es H-Shem b’simcha” serve H-Shem in joy (100:2)? Even in such dark times, Esther still felt that one should strive to find joy in serving H-Shem, and combat annihilation that way.
Similarly, according to Rav Pam, the events in this verse point to a fundamental difference between Esther and Mordechai regarding their approach to defending Judaism in exile.
He quotes the Megillas Sesarim who writes that Esther felt we should use teshuva together with political maneuvering to effect change. Mordechai, on the other hand, felt we should fulfill the words of the wisest of men, who wrote, “When a person’s ways are desirable for H-Shem, even his enemies seek peace with him” (Mishlei 16:7). In other words, all we must do is attempt to be the best we can be, and H-Shem will protect us from any potential enemy.